1. Field of the Invention
The present invention is in the field of making commutators for electrical motors. More particularly, this invention is in the field of carbon commutators for electric fuel pumps operating in an environment of single- or multiple-component hydrocarbon fuels with a significant portion of oxygen-containing moieties.
2. Description of the Prior Art
Electric fuel pumps have long been used in automotive applications to effect movement of liquid fuels from the storage means to the engine. Early pumps were simply the application of electrical energy to a mechanical pump; later pumps incorporated the motor and pump mechanism, but maintained the isolation of the fuel from the motor.
While mechanical pumps generally are located near the engine, and serve primarily as suction devices, electric fuel pumps function best as pressure pumps, and are most often located very near the fuel tank. Present technology often provides a fuel pump submerged inside the fuel tank, with the electric motor operating in the liquid fuel itself, thus eliminating the need for shaft seals or any other mode of isolation of the motor from the environment.
Electric fuel pumps operating in a substantially pure hydrocarbon environment, i.e., gasoline or diesel fuel, are known in the art, and have acceptable operating lives. In U.S. Pat. No. 4,399,383, Kamiyama discloses a gasoline-resistant commutator having a silver current-carrying medium plated or clad onto a copper substrate to minimize wear on the commutator surface by the motor brushes working submerged in a gasoline tank. The Kamiyama patent, however, is restricted by its terms to operation in an ordinary gasoline environment, and its efficacy in other media is unpredictable.
In more recent times, the advent of mixed fuels with a significant portion of oxygen-containing moieties, e.g., methanol or ethanol, added to the base hydrocarbon, has lead to problems with the rapid wear of the commutators of conventional submerged electric fuel pumps. It has been determined that the Kamiyama device is only moderately suitable in such other types of environments containing significant amounts of hydroxylic components. While not wishing to be bound by theoretical considerations set forth herein, it is believed that copper and other metals, under the influence of highly localized electrical fields such as those encountered with interface sparking or current transfer, react with the hydroxyl group of an alcoholic fuel moiety or water dissolved therein, thus producing the respective metal salt which is then carried into the fuel stream. Continuously repeated reactions of this sort drive the equilibrium of the equation of that reaction to the right, causing a comparatively rapid removal of the metal until the commutator surface is worn beyond utility, leading to unacceptably short service life of the fuel pump.
While submerged fuel pumps have been used with acceptable service lives in environments consisting essentially of gasoline with only minor amounts of additives such as octane enhancers, anti-gum agents and the like, the increasing occurrence of oxygen-containing fuels, specifically alcohols, has lead to high rates of wear on copper commutators. With a continuing emphasis on matters of concern for the environment, there is a substantial likelihood that fuels consisting primarily of gasoline may be replaced entirely or in part by oxgeyn-containing liquid fuels such as, e.g., methanol and ethanol. Under these circumstances, submerged fuel pumps with metallic, e.g., copper commutators will be unsatisfactory.